In the shaping of bar, tube and rod stock of metal, especially steel and nonferris metals, a drawing device can be used in which a carriage engages the workpiece downstream of a die and displaceable to pull the workpiece through the die. The finished products which result have precise dimensions and a good finish and can be bars of various configuration, tubes and wire or rod with precise external dimensions. The die or drawing ring is generally stationary and downstream of the die a cutoff device can be provided for cutting the drawn product into desired lengths.
Drawing apparatus of the afore-described type, as hitherto provided, can be divided into two groups. One group encompasses drum-type drawing machines while the other encompasses linear drawing machines.
In the category of linear drawing machines, it is known to provide two counter movable drawing carriages, one of which is displaceable in a direction away from the die while engaging the workpiece to pull the workpiece through the die while the other returns from its maximum excursion position to a location close to the die so as to be ready to engage the workpiece. The workpiece is pulled through the die, therefore, by a hand over hand action.
In another arrangement, two countermoving circulating endless drawing chains are provided which can be coupled with and decoupled from the workpiece.
Such drawing machines, often referred to as caterpillar or track drawing machines are described for example in European documents EP 0 548 723 B2 and EP 0 814 921 B1.
They have, by comparison to the hand over hand type of drawing machine the advantage that the endless chains can move more uniformly and in one direction and thus do not need to intermittently accelerate a mass with the detrimental effect that that may have on an apparatus.
In the finishing stages of the fabrication of tubes, structural shapes and semifinished bar products of steel and nonferris metal products, there are various advantages it providing a drawing bench or the like for drawing the workpiece and then cutting it to specific lengths. The two-slide or two-carriage machines require either flying cutoff devices or like systems in which over a length of from 4 to 6 meters, a cutoff tool may have to be moved along with the workpiece.
The linear drawing benches of the prior art, in addition, generally allow only a limited stroke of the alternatingly moving carriages and thus multiple strokes for a given finished length of the drawn product. This is the case with hand over hand operation as has been described. The processing is generally discontinuous and the machine must therefore be capable of withstanding high inertias.
Another drawback of earlier drawing benches is that they are relatively prone to failure, have high maintenance and repair cost and have lower productivities than may be desirable. The flying saw or other cutoff devices is comparatively expensive and contributes to the high operating, maintenance and capital cost.